Cause: Data saving error during undervoltage comes when the inverter failed to save data such as the frequency commands and PID commands (which are specified through the keypad), or the output frequencies modified by the UP/DOWN terminal commands when the power was turned OFF.

erf fault in fuji FRENIC MEGA drive indicates Data Saving Error during Undervoltage. This means the drive tries to save operational data or parameters during a power-down, but the DC bus voltage dropped too quickly (undervoltage), preventing a successful write to memory.

• Check how long it takes for the DC link bus voltage to drop to the preset voltage when the power is turned OFF.
• Check if noise control measures are appropriate (e.g., correct grounding and routing of control and main circuit wires).
• The control circuit failed. If erf occurs each time the power is turned ON.